242 PHYSICS. 



began to crepp away from the glass, scarcely wetting it, and no doubt 

 was entertained that soon the phenomenon seen in Quincke's tubes would 

 appear, and the acid would roll about in the tube like mercury. The 

 explanation is that these peculiar capillary phenomena are due to a thick 

 layer of gas that is condensed over the surface of the glass. — {Nature, 

 XX, 291, 1880.) 



De la Rue and Miiller, reasoning from their electric researches on the 

 spark in rarefied air, believe themselves entitled to conclude on the 

 probable height of our atmosxjhere. The least resistance to an electric 

 discharge in hydrogen is obtained at a pressure of 0.642™™, or 845 M 

 (M signifying millionths of an atmosphere). When it reaches .002™™, or 

 .3 M, the discharge only just passes with a potential of 11,000 silver chloride 

 cells (11,330 volts). At the highest exhaustion, 0.000055™™, or 0.066 M, 

 no discharge took place with the 11,000 cells, but even a 1-inch spark 

 failed to pass. Since a discharge at atmospheric pressure which occurs 

 in hydrogen at 0.22 inch takes place in air only at 0.13 inch, the authors 

 •conclude that the least resistance for air is at 0.379™™, or 408.6 M. This 

 pressure would be reached at a height of 37.67 miles above the sea. 

 Hence here the auroral discharge would have its maximum brilliancy, 

 .and would be visible 585 miles. The best vacuum produced, 0.066 M, 

 corresponds to a height of 81.47 miles. At this height the discharge 

 would be considerably less brilliant. At a height of 124.15 miles the 

 pressure would be only .00000001™™, or 0.00001 M, and at such a height 

 it is not conceivable that a discharge would occur with any probable 

 potential. At a pressure of 62™™ the discharge has the weil-known car- 

 mine tint of the aurora. This corresponds to an altitude of 12.4 miles. 

 At a pressure of 1.5™™ it becomes salmon-tint, and at 0.8™™ much paler. 

 Above this exhaustion it becomes a pale milky white. — {Mature, xxi, 33, 

 1880.) 



Debrun has suggested an improved barometer, which he calls an 

 .amplifying barometer. It resembles the Fortin instrument in general, 

 but the iDoint marking the zero is at the top of the tube. The cistern 

 has a second tube in its top, open to the air, and into which the mercury 

 rises, so that the reading is the difference of the levels of the mercury 

 surfaces in the two tubes. A third and narrower tube, also open at top, 

 passes through the top of the cistern. This cistern is larger than ordi- 

 nary, and contains water above the mercury, into which this tube dips, 

 and which rises into it, the level being read by means of a graduat-ed 

 scale. Any variation of the height of the mercury is multiplied in the 

 water-column in the ratio of the section of the cistern to that of the 

 water- tube. Hence the sensibility of such a barometer is equal to that 

 of the water-barometer. — {J. Phys., ix, 387, November, 1880.) 



Jordan has constructed and erected in the Kew Observatory a barom- 

 eter in which the liquid employed is glycerin colored with aniline-red. 

 As manufactured by Price & Co, the glyceriu has a si^ecific gravity ot 

 1.26. Hence the mean height of the column is 27 feet, and a variation 



